The present invention relates to an electromechanically or pneumatically actuable disc brake, in particular for a commercial vehicle.
A generic disc brake is known from WO 02/14708, which disc brake can be embodied as a sliding caliper brake, a pivoting caliper brake and/or as a fixed caliper brake with a stationary or moveable, in particular displaceable, brake disc.
During braking, an actuation of the brake application device takes place, during which, in the case of a fixed caliper brake, initially the application-side brake lining is pressed against the brake disc and then the moveable brake disc is pressed against the reaction-side brake lining.
Here, the application-side brake lining is displaced by one, or preferably two, brake pistons which engage thereon. The brake pistons, on the other hand, function as adjustment pistons as constituent parts of adjustment devices, by which an air play between the brake pads and the brake disc can be set. Adjustment devices on both sides of the brake disc reduce the path which the disc and/or caliper must move through, since the wear travel can be compensated by way of the adjustment devices alone.
In WO 02/14708, the adjustment devices on one or both sides are, preferably, driven electromechanically, with the electric motor being designed such that the brake piston can move the brake lining towards and away from the brake disc by use of pressure pieces.
As a result, in particular of the often very harsh operating conditions under which the disc brakes are used, the functional capability of the disc brakes can under certain circumstances be restricted, that is to say operational readiness is not optimally provided at all times and under all conditions.
The resulting problems include that it is not always ensured that the brake linings are released from the brake disc, in particular when the brake linings are, so to speak, “baked” on to the brake disc as a result of corrosion.
In addition to the very high degree of wear of the brake disc and/or of the brake linings caused as a result, the functional safety of the disc brake can also be adversely affected under some circumstances without corresponding countermeasures being taken.
Here, the adhesion forces with which the brake linings adhere to the brake disc as a result of corrosion can be so large that the return force of the electric motor of the adjustment device alone is not sufficient to release the brake linings from the brake disc.
However, even in the case where the brake linings release from the brake disc, a defined release is desired, in particular when the brake disc is mounted in an axially moveable fashion such as in the case of a fixed caliper brake. As a result of the undefined position of the brake disc and/or of the brake caliper in a sliding caliper brake, it is not possible to entirely prevent the brake linings from grinding against the brake disc.
This naturally leads to an increased degree of wear both of the brake linings and of the brake disc, which hinders an optimum service life of the disc brake.
In addition, the increased driving resistance resulting from the friction of the corresponding components in the unbraked position leads to increased fuel consumption, which also hinders the desire to minimize operating costs.
The present invention is, therefore, based on the need to further develop a disc brake of the above-mentioned type in such a way as to improve its operational reliability.
This, and other, needs are provided according to the invention by an electromechanically or pneumatically actuable disc brake, in particular for a commercial vehicle, having a brake caliper which engages over a brake disc, a brake application device, which is arranged in the brake caliper, for applying the brake by way of at least one, or a plurality of, brake pistons which each bear against brake pads having brake linings, at least one electromechanically drivable adjustment device for adjusting an air play between the brake pads and a brake disc, wherein an electric motor is preferably operatively connected to the associated brake piston for operating the adjustment device. The at least one brake piston and/or the pressure piece is arranged, so as to be releasable to a limited extent, on the associated brake pad by way of spring elements, which are deflectable in the displacement direction.
According to the invention, the at least one brake piston and/or the pressure piece is arranged, so as to be releasable to a limited extent, on the associated brake pad by way of spring elements, which can deflect in the displacement direction. In the case of adjustment devices being arranged on both sides of the brake disc, such an arrangement is preferably provided on both sides of the brake disc.
It is achieved according to the invention that the brake piston, together with pressure pieces, can be released to a limited extent from the brake pads at all times, that is to say even when the return forces of the electric motor of the adjustment device are not sufficient to release the brake pads, which are fixedly adhered to the brake disc.
In a worst case, there is grinding contact between the brake pad and the brake disc, but never a situation in which the brake pistons are prevented from releasing from the brake disc.
Normally, the vibrations which occur during normal driving operation are sufficient to separate the brake pads. This, of course, also includes their return movement, which requires free mobility in the direction away from the brake disc, and is now provided.
For fault-free, that is to say “normal” functioning, the brake piston assigned to the spring element bears against the brake pad under a preload of the spring element, so that a so-called elastic connection is provided between the brake piston and the brake pad, which is released only in a certain dimensional range, when the return forces of the electric motor are not sufficient to release the brake pads from their frictional position.
Here, the spring element, preferably a clamping spring embodied as a leaf spring, is dimensioned such that the spring force is lower than the return forces of the electric motor which drives the brake piston.
A mechanical retraction block is preferably provided for delimiting the return path of the brake piston, which retraction block delimits the stroke of the electric motor, so that a maximum value of the air play is not exceeded, since the brake could otherwise become ineffective.
In order that the functional capability of the retraction block is not adversely affected, when the brake pad does not release from the brake disc after the preload force has been overcome by the return of the electric motor, the spring element preferably bears against a stop (or itself forms a path-delimiting stop), whose distance from the spring element in the normal position is determined by the maximum permitted air play. Since the spring path is delimited by the stop, the adjustability of the brake piston together with the pressure piece is likewise delimited, with the maximum air play dimension between the brake piston and the brake pad corresponding to that between the brake pad or its friction face and the brake disc in the case that the brake pad is released correctly from the brake disc.
According to an advantageous aspect of the invention, a stop is arranged on a positionally fixed component, against which stop the brake disc and/or the brake caliper bears under elastic preload in the released state of the brake.
This ensures that, when the brake application device is released, a free play between the brake pads and the brake disc is inevitably formed by the elastic force, with the result that grinding of the brake disc against the brake pads during driving, and the resulting increased degree of wear and increased fuel consumption, are prevented.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.